Method for cross-linking rubber

ABSTRACT

Rubber is cross-linked by heating with compounds of the formula (Acc-SSx)nR wherein Acc-S- is an accelerating moiety, R is an organic bridging group and n is two or more. If it is postulated that cross-link formation results from direct reaction of accelerator polysulfide intermediates via a concerted mechanism and that there is ultimately formed from reaction of accelerator and sulfur a polysulfide, Acc-SSx-S-Acc, the simplest cross-linking reaction involves formation of rubber intermediate combining the accelerator moiety followed by formation of sulfur cross-linked rubber and regeneration of the accelerator moiety. Consistent with these postulations, crosslinking of rubber is described with a compound containing two Acc-SSx- groups connected through the organic bridging group R which becomes part of the cross-link.

tinned States Patent 1191 1111 3,869,435

Trivette, Jr. Mar. 4, 1975 [5 METHOD FOR (CROSS-LINKING RUBBER 2,619,481 11/1952 Baldwin 260/795 2,983,716 5/1961 F' 1d 260 79.5 [75] Inventor: f Trvette Akron 3,468,855 9/1969 Him; 260793 01110 3,705,923 12/1972 Sullivan 260/608 [73] Assignee: Monsanto Company, St. Louis, Mo.

, Primary ExaminerChristopher A. Henderson, Jr. [22] 1971 Assistant ExaminerC. A. Henderson, Jr. [21] Appl. No.: 200,595

[57] ABSTRACT 260/79-5 C, 252/1841 260/795 Rubber is cross-linked by heating with compounds of 260/79-5 1 260/248 260/2495 260/251 the formula (AccSS,),,R wherein Acc-S- is an ac- QA. celerating moiety, R is an organic bridging group and 1 1 a n is two or more.

260/306 If it is postulated that cross-link formation results from R 5 S 260/783 260/784 260/785 direct reaction of accelerator polysulfide 260/787 260/934: intermediates via a concerted mechanism and that [5 I} Int Cl C08c 11/54 Cosd 9/00 b 27/06 there is ultimately formed from reaction of accelerator [58] Fie'ld 266/79 5 R B 79 5 C and sulfur a polysulfide, Acc--SS,SAcc, the 260/775 5 6 simplest cross-linking reaction involves formation of 306 g 5 307R D rubber intermediate combining the accelerator moiety S R 4 5 QA 2564 0 followed by formation of sulfur cross-linked rubber 294 8 294 8 2 and regeneration of the accelerator moiety. Consistent with these postulations, cross-linking of rubber is 56 R f Cited described with a compound containing two Ace-SS,- 1 e erences groups connected through the organic bridging group UNITED STATES PATENTS R which becomes part of the cross-link. 2,422.56 6/1947 Wolf 260/795 2,598,407 5/1952 Marvel 260/225 16 Clalms, N0 Drawlngs METHOD FOR CROSS-LINKING RUBBER This invention relates to methods and compounds useful for cross-linking rubber. More particularly, it relates to a new cross-linking reaction capable of producing thermally stable vulcanizates having a high proportion of monosulfidic cross-links.

BACKGROUND OF THE INVENTION vulcanization of rubber normally gives sulfidic crosslinks in allylic position with respect to a double bond in the vulcanizate coupled with some cyclization instead of cross-linking as well as other undesirable side reactions. When elemental sulfur is the vulcanizing agent the cross-links are mainly polysulfidic and it is now recognized that polysulfidic cross-links as compared to monosulfidic cross-links reduce thermal stability of the vulcanizate. There have been suggestions to modify the cross-linking reaction by reacting rubber with dithiols to introduce an organic bridging element into the cross-link. However, dithiols add across double bonds of adjacent rubber molecules reducing unsaturation by a cross-linking reaction different from the classical vulcanization reaction. .I. LeBras, Kautschuk U. Gummi, VIS, WT 407-WT 418 (1962), FIG. 14; G. E. Meyer et al., Rubber World, V136, 529 (1957); C. M. Hull. Ind. Eng. Chem, V40, 513 (1948). Ifa derivative of mercaptobenzothiazole is used as the accelerator in the classical vulcanization reaction with elementa] sulfur it is known that mercaptobenzothiazole is generated in the process. Some theories devised to explain the mechanism of cross-linking rubber by the action of elemental sulfur and organic accelerator which is a merceptan or derivative thereof assume that the accelerator reacts with sulfur to form polysulfide (herein meaning two or more sulfur atoms) and propose a cross-linking scheme involving free radical intermediates whereby a rubber polythiyl radical cross-link precursor forms which reacts preferentially with the polysulfide until all is combined with the rubber, then cross link formation beings. Coran, Rubber Chem. Technol. 37, 689 1964). The theory is capable of explaining observed kinetics of vulcanization but it is difficult to write satisfactory steps for the actual cross-linking process itself. In vulcanization of diene rubber with tetramethylthiuram disulfide, evidence for formation of a rubber bound intermediate SUMMARY OF THE INVENTION If it is postulated that cross-link formation results from direct reaction of accelerator polysulfide intermediates via a concerted mechanism and that there is ultimately formed from reaction of accelerator and sulfur a polysulfide, Acc-SS S-Acc, the simplest crosslinking reaction is Acc-SS -S-Acc Rubber Rub-S -S-Acc Ace-SH Rub-S S-Acc Rubber .Rub-S,-Rub Acc-SH Consistent with the foregoing scheme it has now been found that a compound containing two Ace-SS,- groups connected through an organic bridging group R is a primary vulcanizing agent, R of which becomes part of the cross-link and the sulfur in the cross-link is monosulfidic if x is one. The cross-linking function with unsaturated rubber may be illustrated as follows:

Experimental results are consistent with the foregoing scheme of vulcanization. Although the invention is not limited to any theory by which cross-links form there can now be no doubt that compounds of the aforesaid characteristics comprise a general class of primary cross-linking agents. The mechanisms and the nature of the cross-links are undoubtedly more complex than illustrated and the cross-link may, for example, involve multiples of (SRS).

Accordingly, the present invention provides a new cross-linking reaction wherein organic bridging groups are introduced into the cross-link in allylic position. The adjuvants for effecting said reaction which are for the most part new compounds, may be represented by the formula (Acc-SSQ R-S -S-Acc wherein Acc-S- is the same or different accelerating moiety, 2: is l, 2, 3 or 4, n is l, 2 or 3 and R is an organic bridging group of valence n l. Accelerating moiety refers to a nucleus contained in compounds which accelerate the vulcanization of natural and synthetic diene rubbers. Organic mercaptans, disulfides and other mercaptan derivatives have been widely used to accelerate vulcanization of rubber. Well known mercaptans or mercaptan derived accelerators are represented by the formula Acc-S-M where M is typically hydrogen, metal or in the case of disulfides, is Acc-S- and Accis the residue of an accelerating mercaptan. The mercaptan and mercaptan derived accelerators may be conveniently represented as containing the moiety Acc-S- and it willbe noted that at least two such moieties are present in the new cross-linking agents and are linked through at least one additional sulfur atom to an organic bridging radical. The accelerating moiety will usually be the same but may be different and sometimes different accelerating moieties are advantageous.

An exhaustive discussion of mercaptans and derivatives known for accelerating vulcanization of rubber is unnecessary for an understanding of the invention. The accelerating moiety may be the residue of any mercaptan which enhances the vulcanization rate of diene rubber with sulfur. Illustrative of well known classes of accelerators from which the accelerating moiety may be derived are Z-mercaptoazoles, dithiocarbamates, phosphorodithioates and xanthates. Others will be discussed hereinafter and all of them copiously illustrated although it will be appreciated that the accelerating moiety per se is in general well known.

The organic bridging group R is largely a matter of choice. Selection of particular R groups is unnecessary for effecting the cross-link reaction but the R group in the cross-linking agent will exert some influence on the efficiency of the cross-linking reaction and on scorch and cure rates. Of course, it might be possible to find functional bridging groups which would defeat the purpose of the invention but it is assumed that no one would desire to obtain a useless result and that no one will be misled by the permissible wide variation in R. This great variety of R groups found useful renders it impossible to define them in simple structural form and language to designate the genus is non-existent For convenience, it will be understood that the term organic bridging groups" as used herein means the organic radicals described herein for purposes of illustrating R. It is believed, however, that equivalents will be readily suggested therefrom. For example, no reason appears why R must be confined to any particular number of carbon atoms and R groups of fifty or more carbon atoms would still be expected to provide useful results.

Illustrative of azole radicals which are suitable for Acc in the above formula are oxazole, imidazole and thiazole represented by the formula wherein the unsatisfied valences on the vicinal carbon atoms are attached to hydrogen, lower alkyl, benzyl, acetyl, carboalkoxy and phenyl or together with the carbon atoms forms an alicyclic ring or an ortho arylene ring, or two of the unsatisfied valences are joined to form a double bond. The ortho arylene ring may be substituted by lower alkyl, halo. nitro, hydroxy, carboalkoxy, acetyl, lower alkoxy and phenyl radicals, and X is S, O or NH. Lower alkyl means radicals containing 1-5 carbon atoms.

Specific examples of azole radicals in the crosslinking agents are Z-thiazolyl, 2-thiazolinyl, 2-oxazolyl, 2-oxazolinyl, Z-imidazolyl, Z-imidazolinyl, 2- benzothiazolyl, 2-benzoxazolyl, 2-benzimidazolyl, 2- naphthathiazolyl, Z-dihydrobenzothiazolyl, 2-(4,5,6,7- tetrahydrobenzothiazolyl), 2-(4-methylthiazolyl), 2-(4- methyloxazolyl), 2-(4-methylimidazolyl), 2-(4- ethylthiazolyl), 2-(4-ethyloxyazolyl), 2-(4- ethylimidazolyl), 2-(4-n-propylthiazolyl), 2-(4-npropyloxazolyl, 2-(4-n-propylimidazolyl), 2-(4-nbutylthiazolyl), 2-(4-n-butyloxazolyl), 2-( 4-npropylimidazolyl), 2-(4,5-dimethylthiazolyl), 2-(4,5- dimethyloxazolyl), 2-(4,5-dimethylimidazolyl), 2-(4,5- diethylthiazoly), 2-(4,5-diethyloxazolyl), 2-(4,5- diethylimidazolyl), 2-(4,5-di-n-pr0pylthiazolyl),

2-(4,5-di-n-propyloxyazolyl), 2-(4,5-di-npropylimidazolyl 2-( 4,5 -di-n-butylthiazolyl 2-(4,5-di-n-butyloxazolyl), 2-(4,5-di-nbutylimidazolyl), 2-(4,5-diphenylthiazolyl), 2-(4,5- diphenyloxazolyl), 2-(4-phenylimidazolyl), 2-(4- phenyl-S-methylthiazolyl), 2-(4-phenyl-5- methyloxazolyl), 2-( 4-phenyl-5-methylimidazolyl), 2- (5-acetyl-4-methylthiazolyl), 2-(5-carbomethoxy-4- methylthiazolyl), 2-(5-carbethoxy-4-methylthiazolyl), 2-(S-carbethoxythiazolyl), 2-(5-carbamoyl-4- methylthiazolyl), 2-(5-carbanilino-4-methylthiazolyl), 2-(4-ethylbenzothiazolyl), 2-(4-ethylbenzoxazolyl), 2-(4-ethylbenzimidazolyl), 2-(5-chlorobenzothiazo'lyl). 2-(5-chlorobenzoxazolyl), 2-(5-chlorobenzimidazolyl), 2-(-ethoxybenzothiazolyl 2-(6-ethoxybenzoxazolyl),

2-(o-ethoxybenzimidazolyl), 2-(4-phenylben2othiazolyl). 2-(4-phenylbenzoxazolyl), 2-(4- phenylbenzimidazolyl), 2-(5-carbethoxybenzothiazolyl), 2-(S-carbethoxybenzoxazolyl), Z-(S-carbethoxybenzimidazolyl), 2-(6-nitrobenzothiazolyl), 2-(6- nitrobenzoxazolyl), 2-(6-nitrobenzimidazolyl), 2-(4-methylbenzothiazolyl), 2-(4-methylbenzoxazolyl). 2-(4-methylbenzimidazolyl), 2-(5-ethylbenzothiazolyl), 2-(5-ethylbenzoxazolyl), 2(5- ethylbenzimidazolyl). 2-(6-tert-butylbenzothiazolyl), 2-(fi-tert-butylbenzoxazolyl), 2-(6-tertbutylbenzimidazolyl), 2-(4,6-dimethylbenzothiazolyl), 2-(4.6-dimethylbenzoxazolyl). 2-(4.6-dimethylbenzimidazolyl). 2-(5,o-diethylbenzothiazolyl), 2-(5,6-dicthylbenzoxazolyl), 2-(5.6-diethylbenzimiclazolyl), 2-( 7-methylbenzothiazolyl), 2-(7-methylbenzoxazolyl), 2-(7-methylbenzimidazolyl), 2-(o-octylbenzothiazolyl), 2-(6-octylbenzoxazolyl), 2-(o-octylbenzimidazolyl), 2-(4-methylthiazolinyl), 2- (S-methylthiazolinyl), 2-(4,4-dimethylthiazolinyl), 2-(5,S-dimethylthiazolinyl), 2-(4-ethylthiazolinyl), 2- (4-butylthiazolinyl), 2-(4-methyl-S-butylthiazolinyl), 2-(4-phenylthiazolinyl), 2-(4-benzylthiazolinyl), 2-[4- (Z-hydroxyethyl)-thiazolinyl], 2-(4-chloro-5- methylthiazolinyl), 2-(4-chloro-5-ethylthiazolinyl), 2-(4-hydroxythiazolinyl), 2-(4-methoxythiazolinyl), 2-(4-aminothiazolinyl), 2-(5-chlorothiazolinyl),

2-(5,5-dimethyloxazolinyl), 2-(4,5- dimethyloxazolinyl), 2-(4-ethyloxazolinyl), 2-( 5- ethyloxazolinyl), 2-(4-methyloxazolinyl), 2-(4,4- dimethyloxazolinyl), 2-(4-phenyloxazolinyl), 244- methoxyoxazolinyl), 2-(4-butyloxazolinyl) and 2-(5- amyloxazolinyl). Of the azole radicals, thiazolyl radicals and especially benzothiazolyl are preferred.

The characteristic moiety present in dithiocarbamates and structurally related accelerators suitable for Acc is represented by the formula wherein R and R independently are hydrogen, alkyl, cycloalkyl, aralkyl, phenyl, substituted phenyl and R, and R along with the nitrogen atom may form a heterocycle of 4-8 carbon atoms and X" is S or 0 but S is much preferred and R, and R of 1-20 carbon atoms are preferred within which group 4-20 carbon atoms are more preferred in order to minimize or eliminate surface bloom on the vulcanizate. Examples of R, and R are methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, hexyl, octyl, decyl, dodecyl, eicosyl, cyclopentyl, cyclohexyl, cyclooctyl, phenyl, benzyl, phenethyl and tolyl.

Specific examples of thiocarbamoyl radicals of the preferred dithiocarbamates are N,N-(dimethyl)thiocarbamoyl, N,N-(diethyl)thiocarbamoyl, N,N-(di-npropyl)thiocarbamoyl, N,N-(di-n-butyl)thiocarbamoyl, N,N-(di-hexyl)thiocarbamoyl, N,N-(di-octyUthiocarbamoyl, N,N-(di-decyl)thiocarbamoyl, N,N-(didodecyl)thiocarbamoyl, N-octadecyl-N-isopropylthiocarbamoyl, N,N-(dfbenzyUthiocarbamoyl, N-ethyl- N-benzylthiocarbamoyl, N-hexyl-N-benzylthiocarbamoyl, N-methyl-N-cyclohexylthiocarbamoyl, N,N- (dicyclohexyl)thiocarbamoyl, N-methyl-N-phenylthiocarbamoyl, N-ethyl-N-phenylthiocarbamoyl, N- propyl-N-phenylthiocarbamoyl, N-benzyl-N-phenylthiocarbamoyl,

and

P- R O wherein R and R independently are alkyl, cycloalkyl, aralkyl, phenyl and alkyl substituted phenyl. Examples of R and R are methyl, ethyl, propyl, isopropyl, nbutyl, isobutyl, sec-butyl, tert-butyl, n-amyl, hexyl, octyl, decyl, dodecyl, eicosyl, cyclopentyl, cyclohexyl, cyclooctyl, phenyl, benzyl, phenethyl and tolyl. Each of R and R will usually contain lcarbon atoms and alkyl radicals of l-6 carbon atoms comprise a preferred subgroup.

The characteristic moiety present in xanthate anad structurally related accelerators suitable for Acc is represented by the formula wherein R preferably contains l20 carbon atoms and is alkyl, cycloalkyl, aralkyl, phenyl and alkyl substituted phenyl and X" is S or 0, preferably S. Examples of R are methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, hexyl, octyl, decyl, dodecyl, eicosyl, cyclopentyl, cyclohexyl, cyclooctyl, phenyl, benzyl, phenethyl and tolylr There are of course other classes of thio accelerators well known to the art. Merely by way of illustration, other Acc radicals along with the sulfur atom to which they are attached which may be mentioned as suitable accelerator moieties in the new cross-linking agents are 2-pyrimidinylthio, 2-(4,6-dimethyl-pyrimidinylthio), 2-(4,4,6-trimethyl-dihydropyrimidinylthlo), 2- tetrahydropyrimidinylthio, 4-benzopyrimidinylthio, 4- l2,6dimethyl-pyrimidinylthio), 4-(6- methoxypyrimidinylthio), 4-(6-methyl-2-methylthiopyrimidinylthio), 4-(5-methoxy-pyrimidinylthio), 2-(4- methyl-o-phenyLpyrimidinylthio), 2-(4-methylpyrimidinylthio), 2-(4-methylthio-pyrimidinylthio), 2- lS-nitro-pyrimidinylthio), 2-(4- methylaminopyrimidinylthio), 2-(6-methylaminopyrimidinylthio), 2-(4-morpholino-pyrimidinylthio), 4-quinazolinylthio, dithiole-3-thionc-5-ylthio, 2-[4,6- bis(ethylamino)I-s-triazinylthio, 2-[4,6-bis(isopropylamino)l-s-triazinylthio, 2-(4-ethylamino-6-dicthylamino)-s-triuzinylthio, 2-[4,6-bis(phcnyl)]-striazinylthio, 2-(4-chloro-6-phenyl)-s-triazinylthio, 2,4-

6 dinitrophenylthio, 2-nitrophenylthio, 2-chloro-4- nitrophenylthio, 2-( S-acetamido-l ,3 ,4- thiacliazolylthio), 2-(4-phenyl-5-thioxo-1,3,4- thiadiazolylthio), 5-( 3-bromo-l ,2,4-thiadiazolylthio),

5-(3-chloro-1,2,4-thiadiazolylthio), Z-pyridinylthio, N- (dialkylamino)thiocarbamoylthio (derived from, e.g.,

1,l-dimethyldithiocarbazinic acid) and 2- quinolinylthio.

Suitable accelerator moieties where Acc-S- is pyrimidinylthio will perhaps be better understood from the formulas wherein R R and R independently are hydrogen, lower alkyl, lower alkoxy, phenyl, nitro, chloro, lower alkylthio, lower alkylamino, lower dialkylamino, heterocyclic amino or R and R together with the adjacent carbon atoms to which they are attached form ortho arylene. The corresponding dihydro or tetrahydro pyrimidinylthio radicals may be used where desired.

Similarly, the s-triazinylthio radicals may be represented by the formula wherein R and R are independent and independently have the same meaning as before.

Formulas representative of thiadiazolylthio radicals in the cross-linking agents are t R -N N M ll EC-S- or 10 I c-ss==c s c-ss==c crt Typical aminodithiocarbamoyl radicals have the formula 5 (lower a1kyl) N NH S Representative pyridinylthio AccS radicals have the formula wherein each R independently is hydrogen or lower alkyl. The 2-quinolinylthio radical has the formula ca ca m c c-sca ca AccS- derived from nitrothiophenol accelerators are nitrophenylthio radicals of the formula wherein independently each R is hydrogen, alkyl, chloro, nitro, carboalkoxy, carboxy or acetyl. Carbomethoxy and carboethoxy are desirable carboalkoxy radicals but dinitrophenyl is preferred.

The organic bridging group R which joins two or more accelerator moieties through one or more sulfur atoms includes di-, triand tetravalent radicals, preferably hydrocarbon, in which each valence is attached to a carbon atom. The bridging group will generally contain l to 24 carbon atoms within which groups of 2 to 12 carbon atoms are preferred. Still more preferred groups are those having 2 to 8 carbon atoms except that some cross-linking agents where R is l to 4 carbon atoms produce vulcanizates having distinctive odor but usually no significant odor is noticed from use of crosslinking agent wherein R contains more than four carbon atoms. Whether R is acyclic or cyclic the chain may be interrupted by atoms other than carbon, especially oxygen or sulfur. Similarly, suitable R groups comprise two or more arylene radicals joined by sulfur or oxygen. Also, hybrid bridging groups having one valence to sulfur from an acyclic carbon atom and another from a cyclic carbon atom either aromatic or alicyclic are entirely feasible. It will be understood that arylene includes substituted radicals which substituents may be lower alkyl, lower alkoxy, nitro, halogen or combination thereof, the term "lower" designating l to 5 carbon atoms.

One subclass of valuable bridging groups are hydrocarbon radicals which are alkylene or alkylidene of the series C,,H substituted derivatives thereof. The chains may be straight or branched and any branching groups may be attached to a terminal carbon atom or attached to a carbon atom within the chain or both. The aforesaid subclass may be designated by the formula (X), where n is l to 24, each X is the same or different and where Z and Z independently are hydrogen, alkyl, cycloalkyl, benzyl or phenyl. Where n is one and at least one of Z and Z is not hydrogen, the radicals are alkylidene radicals. Where both Z and Z are hydrogen in all units present, straight chain alkylene radicals are defined. Illustrative of R when CHI-l2" are divalent radicals derived by removal of two hydrogen atoms from methane, ethane, propane, butane, isobutane, pentane, hexane, heptane and octane.

Another subclass is represented by divalent radicals where both valences are on carbon atoms of the type defined by X supra but the chain is interrupted or substituted in a different manner than described above. This subclass may be represented by the formula where each n" independently is l to 23, m is 0, l or 2. X has the same meaning as before and y is oxygen. sulfur, SO

an: c a n: lower alk l-u:

-C(O)O-, divalent aliphatic cyclic or arylene. Illustrative preferred examples are radicals derived by removal of two hydrogen atoms from each methyl of xylene (phenylenedimethylene).

R also comprises divalent aliphatic cyclic and arylene per se. Thus, a third subclass are divalent cyclic radicals each valence of which is on a carbon atom of an aliphatic ring, said radicals being the residue from redrogen is removed from carbon in two separate monocyclic hydrocarbons joined directly or joined through alkylene or alkenylene not to be confused with the fused ring hydrocarbons. Divalent cyclic radicals preferably contain 5 to 15 ring members and comprise cycloalkylene (saturated monocyclic divalent), cycloalkylidene (two valences on the same carbon), bicycloalkylene, tricycloalkylene (divalent fused rings), bi(monocyclic), such as -C H C H (bicyclohexylene which has the valences on separate cyclic radicals, fused ring radicals having the two valences on the same carbon (bicycloalkylidene and tricycloalkylidene), cycloalkenylene (divalent alicyclic containing unsaturation) and cycloalkenylidene. Illustrative of R when divalent cyclic are radicals derived by removal of two hydrogen atoms from cyclopentane, cyclohexane, cycloheptane, cyclooctane and cyclododecane.

Unsaturated acyclic divalent radicals are suitable bridging groups which subclass are alkylene and alkylidene radicals of the series C H and C,,H (diene radicals).

A wide variety of divalent aromatic radicals are desirable bridging groups which subclass comprise anthrylene and radicals derived by removal of hydrogen from two ring carbon atoms of a compound of the formula and where each Z" independently is hydrogen, lower alkyl, hydroxy, lower alkoxy, acetyl, phenyl, chloro or nitro, Y is oxygen sulfur, SO CO, lower alkylene or lower alkylidene, .r is l to 4. In the thiophene, pyridine and benzene rings, x is 2, 3 and 4, respectively. In the naphthidene ring one x is 2 to 4 depending upon whether or not the two valence bonds are in one ring, the sum of the two xs being 6. Similarly, where two benzene rings are connected, x is 3 or 4 depending upon the position of the two valence bonds and the sum of the two x's is 8. Of the arylene subclass unsubstituted radicals or radicals having only one electronegative substituent are preferred.

Further valuable bridging groups are derived from combinations of the aforesaid radicals which combination may be designated as TT where T is selected from one of the aforesaid subclasses and T is selected from a different member of the aforesaid subclasses and where the free valence ofT is linked to cyclic carbon and the free valence of T is linked to acyclic carbon.

Oxygen substituted bridging groups are represented by straight and branched chain alkylene substituted by one or more oxo, hydroxy, alkoxy, hydroxyalkoxy, alkoxyalkoxy, carboxy, carboxyalkoxy, carboalkoxy or acetoxy substituents. In place of acetoxy other where Y Z and x have the same meaning as before. Suitable trivalent radicals also include those of the formula where A independently is lower alkylene and radicals of the formula where A is lower alkyl and A independently is lower alkylene.

Suitable tetravalent radicals are derived by removal of two hydrogen atoms from any of the aforesaid divalent radicals, for example, C(A'-) where A is lower alkylene which may be regarded as derived from branched chain alkylene, O(-A=) where A is 1,2.3-propanetriyl or other lower alkanetriyl, which radicals may be regarded as derived from interrupted chain divalent radical where (X),." is lower alkylene, Y is oxygen and m is zero and A(OA"=) where A is lower alkylene and A is lower alkanetriyl which may be regarded as derived from interrupted chain divalent radical where (X),,'' is lower alkylene, Y is oxygen and m is one. Still other suitable tetravalent radicals are represented by the formulas where A independently is lower alkylene.

The nature and variety of the bridging group will be further explained by reference to polythiols useful for making the cross-linking agents. R groups when n is 2 are the residues from removing two Sl-l radicals from dithiols. Dithiols useful as intermediates in the prepara tion of the compounds of this invention are 1,1- methanedithiol, 1,2-ethandeithiol, phenyl-l ,2- ethanedithiol, 1,3-propanedithiol, 2,2-propanedithiol, 1,2,-propanedithiol, 2,2-dimethyl-l ,3-propanedithiol, 2-sec-butyl-2-methyl-l ,3-propanedithiol, 1,3-diphenyl- 2,2-propanedithiol, 1,4-butanedithiol, 2,3- butanedithiol, 2,2-butanedithiol, 1,3-isobutanedithiol, 1,5-pentanedithiol, l,6-hexanedithiol, 1,2- hexanedithiol, 2-ethyl-1 ,6-hexanedithiol, 2,5-dimethyl- 3,4-hexanedithiol, 2,5-dimethyl-2,4-hexanedithiol, 2-ethyl-l ,3-hexanedithiol, 3 ,5 ,5 ,-trimethyl-l ,lhexanedithiol, 1,7-heptanedithiol, l,8-octanedithiol, l,2-octanedithiol, 2,6-dimethyl-3,7-octanedithiol, 2,6- dimethyl-2,6-octanedithiol, 1,9-nonanedithiol, l,l'0- decanedithiol, l,l2-dodecanedithiol, 1,2-diphenyl-l ,2- ethanedithiol, 7,8-pentadecanedithiol, 1,10- octadecanedthiol, l,l2-octadecanedithiol, 1,2- hexadecanedithiol, l,2-octadecanedithiol, 1,18- octadecanedithiol, 1,1 l-undecanedithiol and 12,12- tricosanedithiol.

4,8-Dithiaundecane-l ,1 l-dithiol, 4,6-dithianonanel,9-dithiol, 4,7-dithiadecane-l ,IO-dithiol, 2,2- oxydiethanedithiol, 2,2-thiodiethanethiol, 3,3-thiodipropanethiol, 4,4-oxydibutane-l-thiol, 4,4'-oxydipentane-l-thiol, 3,3-oxetanedimethanethiol, 2,2- (ethylenedithio)diethanethiol (HSC H SC H SC H sh), 1,1-cyclohexanedimethanethiol, l,2-cyclohexanedimethanethiol, l,4-cyclohexanedimethanethiol, l,2-bis( 3-mercaptocyclohexyl- )ethylene, l,2-bis(4-mercaptocyclohexyl)ethylene, p-benzenediethanethiol, a, a'-p-xylenedithiol, 2,5- dimethyl-a,a-p-xylenedithiol, 2,3,5,6-tetramethyla,a-p-xylenedithiol, a,oz'-dimethyl-a,a-xylenedithiol and 9,lOanthracenedmethanethiol.

2,2-Camphanedithiol, (1,7 ,7-trimethyl-2,2- dimercaptobicyclo[2.2. 1 lheptane), (2,5-mercaptobicyclo[2.2.l lheptane), 2,5-norbornanedithiol, 2,6-norbornanedithiol, 2-mercapto- S-(mercaptomethyl)norbornane, 2-mercapto-5-(2-mercaptoethyl)- norbornane, 4-mercaptocyclohexaneethanethiol, 2- mercaptocyclohexaneethanethiol, 3- mercaptocyclohexaneethanethiol, 2,2,4,4,-

tetramethyll ,3-cyclobutanedithiol, l, l cyclopentanedithiol, l,2-cyclopentanedithiol, 1,1- cyclohexanedithiol, 1,2-cyclohexanedithiol, 4-cyclohexane-l,2-dithiol, p-dioxane-2,3-dithiol, 1,2- cyclooctanedithiol, p-menthane-2,9-dithiol, 1,1- cycloheptanedithiol, 2-methyl-l,l-cyclohexanedithiol, 4-tert-butyl-l l -cyclohexanedithiol, 1,1- cyclododecanedithiol, l,1-cyclopentadecanedithiol and dimemrcapto derivative of dicyclopentadiene.

2,6-Pyridinedithiol, 3,4-thiophenedithiol, 2,3-thiophenedithiol, 2,5-thiophenedithiol, o-benzenedithiol, m-benzenedithiol, 4-ethoxy-o-benzenedithiol, S-nitro-m-benzenedithiol, 4,5-dimethyl-obenzenedithiol, p-benzenedithiol, 4,5-dimethyl-mbenzenedithiol, 2,4-dimethyl-m-benzenedithiol,

1 1 4-ethyl-m-benzenedithiol, 2,5-dich1oro-mbenzenedithiol, nitro-p-benzenedithiol, 4,4- methylenedibenzenethiol, 4,4'-ethylenedibenzenethiol, 4,4-ethylidenedibenzenethiol, 4,4-isopropylidenedibenzenethiol, 4,4"biphenyldimethanethiol, l,4-bis(mercaptomethyl )napthalene, ,8- bis(mercaptomethyl)tetrahydronaphthalene, 2,4- di(mercaptomethyl)anisole, l,4bis(mercaptomethyl)- 2,5-dimethoxybenzene, tetrachloro-l,4-bis(mercaptomethyl )benzene, 1,4-naphthalenedithiol, 1,5- naphthalenedithiol, 2,6-naphthalenedithiol, 2,7- naphthalenedithiol, 1,2,3 ,4-tetrahydro-2,3- naphthalenedithiol, 2,5-toluenedithiol, dimercapto-o-, m or p-cresol, 5-methoxy-2,4-toluenedithiol, 3,4- toluenedithiol, 2,2'-biphenyldithi0l, 4,4- biphenyldithiol, 3,3'-dimethyl-4,4-biphenyldithiol, 4,4'-sulfonyldibenzenethiol, 4,4'-dithiobenz0phenone, 2,4-dimercaptoacetophenone and 3,5- dimercaptoacetophenone.

Glycol dimercaptoacetate [C H (OOCCH SH) isopropylene glycol dimercaptoacetate [l-lSCH COOCH CH(CH )OOCCH SH], glycol dimercaptopropionate ]C H.,(OOCCH CH SH) HSC H sO H SH, HSC H N(CH )C H SH, HSCH CH N(C H CH SH, HSCH CH N(C H )CH CH SH, C,H NlCH(CH )CH SH] ethene-1,2-dithiol, 2- butene-1,4-dithiol, hexene-l,6-dithiol, 1,3-butadiene- 1,4-dithiol, 2,6-octadiene-l,8-dithiol, 8-cyclododecene-l,4-dithiol, 8-cyclododecene-l,S-dithiol and 9-cyclododccane-1,6-dithiol.

Valuable cross-linking agents are derived from polythiols wherein the residue corresponding to R contains a carboxy, ester, hydroxy, ether or keto substituent. Acid substituents, for example, modify and extend the cross-linking reaction through reactivity with metal 0xides. The synthesis and properties of polythiols which serve as intermediates for cross-linking agents are described by Reid, Organic Chemistry of Bivalent Sulfur, Vol. 1, Chemical Publishing Company, 1958. Others have since appeared in the literature. Examples of polythiol intermediates representative of suitable oxygen substituted bridging groups are 1,3-dimercapto-2- propanol, 2,3-dimercapto-1-propanol, 1,3-dimercapto- 2-methyl-2-propanol, 2,3-, 2,4- or 3,4-dimercapto-lbutanol, 1,3-, 1,4- or 3,4-dimercapt0-2-butanol, 1,4-dimercaptobutanediol-2,3, 2,5- or 4,5-dimercaptol-pentanol, ,2-dimercaptopentanetriol-3,4,5, 1,6-dimercapto-2-hexanol, 2,1 1 -dimercaptol undecanol, l,4-dimercapto-2,3-butandediol, 2,3- dimercapto-1,4-butanediol, and dithioerythritol.

2,6-Dimercapto hexanoic acid, 2,5-bis(3-mercaptopropyl)hexanoic acid, 5,7-dimercapto heptanoic acid, 2,6- or 6,8-dimercapto octanoic acid, 4 or 7 methyl 6,8-dirnercapto octanoic acid, 6,8-dimercapto nonanoic acid 2,3-dimercapto succinic acid, 2,4-dimercapto glutaric acid, 2,5-dimercapto hexandedioic acid, 2,6- dimercapto heptanedioic acid, and 2,7-dimercapto octanedioic acid.

3-Lower alkoxy-1,2-propanedithiol, (2,3-dimercaptopr0poxy)ethanol, (2,3-dimercaptopropoxy)-2- propanol, 3-(dimethoxyethyl)-l,Z-propanedithiol, 3- (2,3-dimercaptopropoxy)-1,2-propanediol, 1-( ,3- dimercaptopropoxy)-3-methoxy-2-propanol, 2,3-dimercapto-l-propanol acetate, 4,5-dimercaptolpentanol acetate, 2,3-dimercapto-l,4-butanediol diacetate, 1,2-dimercapto6,7-dihydroxy4-oxaheptane, 1,-

12 Z-dimercapto-S-hydroxymethyl-6-hydroxy-4- oxahexane, 1,2-dimercapto-3-hydroxy-4- methoxybutane 1,2-dimercapto-3,4,5- trimethoxypentane.

2,3-Dimercapto propanoic acid methyl ester, 2,3- dimercapto propanoic acid, 2,6-dimercapto hexanoic acid ethyl ester, 6,8-dimercapto octanoic acid, 6,8- dimercapto octanoic acid methyl ester, 6,8-dimercapto octanoic acid ethyl ester, 2,3-dimercapto succinic acid, dimethyl, diethyl, diethyl and dipropyl esters of 2,3- dimercapto succinic acid, 2,3-dimercaptopropyl malonic acid diethyl ester, a-(2,3-dimercaptopropyU-oz- (lower all yl)malonic acid diethyl ester, a-(2,3- dimercaptopropyl)-a-(2,3-dihydroxypropyl)malonic acid diethyl ester, a-( 2,3-dimercaptopropyl)-a-( 3-mercaptopropyl) malonic acid diethyl ester, 3,3- dimercapto hexanoic acid ethyl ester, 3,3- dimercaptobutyric acid ethyl ester, 3,3-dimercapt0-2- ethyl butyric acid ethyl ester, 3,3-dimercapto-2-methyl butyric acid ethyl ester, 3,3-dimercapto valeric acid ethyl ester, 2-(1,1-dimercaptoethyl)-valeric acid ethyl ester, 10,1 l-dimercapto undecanoic acid, 2,3-dimercaptopropoxyacetic acid (HSCH CH(SH)CH OCH COOH), B, B-dimercaptoisobutyric acid and B, B'-dimercaptoacetone.

Trithiols and tetrathiols are of course selected as intermediates when it is desired that n of the general formula of cross-linking agents be 3 or 4. Illustrative examples are 1,2,3-propanetrithio, 1,2,3-benzenetrithiol, 1,3,5-benzenetrithiol, trimercapto-m-cresol, 2,4,6- trimercapto phenol, 2,4,6-trimethyl-l,3,5-benzenetrithiol, 1,2,3,4-butanetetrathiol, neopentanetetrathiol, 1,5 1 O-decanetrithiol, tri( Z-mercaptoethyl )amine, 4-mercaptomethylphenyl-3', 4-(dimercaptomethyl(- phenyloxide, 2,2-[4-mercaptomethylpheny1-3, 4'- (dimercaptomethyhphenyl propane, 4-mercaptomethylphenyl-3', 4'-(dimercaptomethyl)phenyl sulphone, 1,3,5-tri(mercaptomethyl)4-methyl benzene, 2,3,4,5- tetra(mercaptornethyl)furan, trimethylolethanetri(3- mercaptopropionate), (CH C(CH OOCCH CH- -SH) trimethylolethanetrithioglycolate, (Cl-l C(CH OOCCH -SH) trimethylolpropanetri(- 3-mercaptopropionate), (CH CH C(CH OOCCH C- H SH) trimethylolpropanetri(thioglycolate), (CH CH flCl-l OOCCl-l -SH) pentaerythritol tetra(3-mercaptopropionate), (C(CH OOCCH C- H SH) pentaerythritol tetrathioglycolate, (C(CH OOCCH SH) and HSCZH OCH -QH-CH OC H SH OC H SH and 3,3'-oxydi-l ,Z-propanedithiol.

Suitable p0ly(oxydialkylene)thiols are described in US. Pat. No. 2,919,262 Nummy, Dec. 29, 1959, which is incorporated herein by reference. Examples of other suitable polythiols are described in US. Pat. Nos. 3,384,671 Louthan May 21, 1968, 3,522,313 Reece et al. July 28, 1970, 3,534,108 Audouze Oct. 13, 1970 and in German Patents 2,004,304 published Aug. 6, 1970, 2,004,306 published Aug. 6, 1970, and 2,004,307 published Aug. 6, 1970.

The following compounds are illustrative of crosslinking agents which are suitable in the practice of this invention.

1, 1 -bis( N ,N-dimethylthiocarbamoyldithio)methane a,a'-bis[ 2( 4.6-dimethylpyrimidinyl )dithio l-p-xylene l,2-bis[ 2( 4.6-dimethylpyrimidinyl )dithio lcyclohexane l,l-bisl2(4.odimethylpyrimidinyl)dithiolcyclohexane 2,9-dil2(4,6-dimethylpyrimidinyl)dithiol-p-menthane l,4-bis[ 2( 4,6-dimethylpyrimidinyl )dithio lnaphthalene 2,5-di[2(4.6-dimethylpyrimidinyl)(dithioltoluene 4,4-bis[2(4,6-dimethylpyrimidinyl)dithio]biphenyl 4,4-bis[2(4.6-dimethylpyrimidinyl)dithioloxybisbenzene bis[2(4.6-dimethylpyrimidinyl)dithiolglycolacetate bisl2(4.6-dimethylpyrimidinyl)dithio1gylcol propionate l,2,3-tri[2(4,6-dimethylpyrimidinyl)dithio1propane l,3.5-tri[2(4,6-dimethylpyrimidinyl)dithiolbenzene tetral2(4,6-dimethy1pyrimidinyl)dithio]neopentane tetra[2(4,6-dimethylpyrimidinyl)dithio]pentaery thritol glycolate 1,l-bis[2(4.6-dimethylamino-s-triazinyldithiolmethane l.2-bis[2(4,6-dimethylamino)-s-triazinyldithio]ethane 1,3bis[2(4.6dimethylamino)s-triazinyldithio]propane l,4-bis[ 2( 4,6-dimethylamino )-s-triazinyldithiolbutane l,6-bis[2(4 6-dimethylamino)-s-triazinyldithiolhexane l ,8-bis[ 2( 4.o-dimethylamino)-s-triazinyldithiloctane l,lO-bis[2(4,6dimethylamino) s-traizinyldithioldecane 1,10-bis[2(4,6-dimethylamino)-s-triazinyldithioloctadecane l l 8-bis[ 2( 4.6-dimethylamino )-s-triazinyldithioloctadecane 2,2'-bisl2(46-dimethylaminol-s-triazinyldithioloxydiethane 2.2'-bis[2(4.6-dimethylamino)-s-triazinyldithio]thiodiethane 4.4'-bis[2(4,6-dimethylamino)-s-triazinyldithio]oxydibutane l.l '-bis[ 2(4,6-dimethylamino )-s-triazinyldithio]-l ,4- cyclohexanedimethane l,4-bis[2(4,6-dimethylamino)-s-traizinyldithio]benzene a.a-bis[2(4,6-dimethylamino)-s-triazinyldithio]-pxylene l,2-bis[2(4,6-dimethylamino)-s-traizinyldithio]cyclohexane 1,l-bis[2(4,6-dimethylamino)-s-triazinyldithio]cyclohexane 2,9-di[2(4,6-dimethylamino)-s-triazinyldithio]-pmenthane l,4-bis[ 2( 4,o-dimethylamino)-s-triazinyldithio lnaphthalene 2.5-di[2(4,6-dimethylamono)-s-tria2inyldithio]toluene 4,4-bisl2(4,6-dimethylamino)-s-triazinyldithiolbiphenyl 4,4'-bis[2(4,6 dimethylamino)-s-triazinyldithio]oxybisbenzene bis[2(4.6-dimethylamino)-s-triazinyldithiolglycolacetate bis[2(4 6-dimethylamino)-s-triazinyldithiolglycol propionate l,2,3-tri[2(4,6dimethylamino)-s-triazinyldithiolpropane l,3.5-tri[2(4.6-dimethylamino)-s-triazinyldithiolbenzene tetrul2(4,6-dimethylamino)-s-triazinyldithiolneopentane 24 tetra[2(4,6-dimethylamino)-s-triazinyldithio]pentaerythritol glycolate l ,1-bis( 2-pyridinyldithio )methane l,2-bis( Z-pyridinyldithio )ethane l,3-bis( 2-pyridinyldithio )propane l ,4-bis( Z-pyridinyldithio )butane l,6-bis( Z-pyridinyldithio )hexane l.8-bis( 2-pyridinyldithio)octane l.l0-bis( Z-pyridinyldithio )decane l,l0-bis( Z-pyridinyldithio)octadecane l.l8-bis( Z-pyridinyldithio )octadecane 2.2'-bis(Lpyridinyldithio)oxydiethane 2,2'-bis(Z-pyridinyldithio)thiodiethane 4,4-bis(Z-pyridinyldithio)oxydibutane l,l-bis( Z-pyridinyldithio )-l .4-cyclohexanedimethane l,4-bis( Z-pyridinyldithio)benzene a,a-bis(Z-pyridinyldithio)-p-xylene l,2-bis( Z-pyridinyldithio)cyclohexane l,l-bis( Z-pyridinyldithio)cyclohexane 2,9-di( 2-pyridinyldithio )-p-menthane l,4-bis( Z-pyridinyldithio )naphthalene 2,5-di(2-pyridinyldithio)toluene 4,4'-bis(2-pyridinyldithio)biphenyl 4,4'-bis(Z-pyridinyldithio)oxybisbenzene bis(2-pyridinyldithio)glycolacetate bis(2-pyridinyldithio)glycol propionate l,2,3-tri( 2-pyridinyldithio)propane 1,3,5-tri(Z-pyridinyldithio)benzene tetra(Z-pyridinyldithio)neopentane tetra(Z-pyridinyldithio)pentaerythritol glycolate The above compounds are illustrative of compounds of the general formula x is one. however, analogous compounds having one or more additional sulfur atoms are included in this invention. The trisulfides are named by changing the dithio in the above compounds to trithio.

The fact that mono and disulfidic cross-links are thermally more stable than higher polysulfidic cross-links accounts for the excellent reversion properties of vulcanizates from cross-linking agents (AccSS ),,R-S,Acc where x is l. The vulcanizate prepared from cross-link agents of the formula (AccSS),,RSSAcc have a substantial proportion of monosulfidic cross-links and considerably higher than vulcanizates prepared with conventional sulfenamide-sulfur cure systems according to the percent of non-reducible cross-links determined by the procedure described by A. Y. Coran, Rubber Chem. and Tech., V37, p 668 (1964).

The amount of cross-linking agent used may vary from 0.1 to 30 parts per parts rubber; normally the amount is 0.5 6 parts per 100 parts rubber with 1.0 4.0 parts being preferred. Generally the modulus of the vulcanizate varies proportionally with the amount of cross-linking agent used.

The cross-linking agents of this invention may be incorporated into rubber by conventional mixing procedures, for example, by adding them in a Banbury mixer or by adding them to the rubber on a mill. Ordinarily with liquid or low melting solid cross-linking agents no special precautions are necessary for obtaining good dispersions. However. when using higher melting crosslinking agents it is recommended that they be ground to a fine powder. preferably 200 mesh or less, to assure adequate dispersion. The cross-linking agent alone effects cross-linking of rubber in the absence of other ingredients but it is preferred to use it in conjunction with conventional compounding ingredients. The rubber stocks may include reinforcing carbon blacks, pigments such as titanium dioxide and silicon dioxide, metal oxide activators such as zinc oxide and magnesium oxide, stearic acid, hydrocarbon softeners and extender oils. amine, ether, and phenolic antidegradants, phenylenediamine antidegradants, tackifiers and phenolic and resorcinol resin adhesive agents. The stocks may also contain prevulcanization inhibitors but in many stocks their use is unwarranted because of the excellent processing safety of the instant cross-linking agents.

ln many applications, the cross-linking agents of this invention will be used without sulfur or accelerating agent. However, for certain applications it is desirable to use them with sulfur, accelerator or both, particularly if very high modulus properties are required. The amount of elemental sulfur will usually be within the range of -15 parts by weight and it is preferred that the amount of elemental sulfur, if present, be within the range of 0.5-1.5 parts per hundred parts by weight of the rubber as characteristic of low sulfur cures. Larger amounts of sulfur result in decreased processing safety and vulcanizates having less reversion resistance. It will be understood that any sulfur-vulcanizing agent may be used in place of sulfur and suitable Vulcanizates obtained with the cross-linking agents of the invention.

Rubber stocks containing the cross-linking agents of this invention may be heated over a wide range of temperatures to effect vulcanization. Generally higher cure temperatures are used with synthetic rubber stocks than with natural rubber stocks. Cure temperatures of 25()550F are suitable with temperatures of 380-350F being more frequently used. The selection of the proper cure temperature depends upon the ingredients in the rubber composition. A compounder may determine the proper curing parameters for any particular stock by testing the composition with an oscillating disk rheometer. The cross-linking agents having thiocarbamoyl accelerating moieties generally require cure temperatures similar to those used in conventional sulfur-sulfenamide accelerator stocks, usually between 280-3 50F. The cross-linking agents having thiazolyl, particularly benzothiazolyl, accelerating moieties are especially adaptable for higher cure temperatures, for example, 300-400F or higher. Certain cross-linking agents with xanthogen accelerating moieties may be cured at lower temperatures, for example, certain rubber compositions may cure at room temperature over several hours. The cure time may be shortened by increasing the temperature; cure temperatures of 100-250F are sometimes advantageous.

The cross-linking agents of the invention are suitable for any rubber having sufficient unsaturation to be sulfur-vulcanizable. Any of the diene rubbers, natural rubber, synthetic rubber or mixtures thereof are suitable. Synthetic rubbers which may be vulcanized by the process of this invention include cis-l,4-polybutadiene, butyl rubber, ethylene-propylene terpolymers, homopolymers of 1,3-butadiene and isoprene such as polybutadiene and polyisoprene, copolymers of 1,3- butadiene with other monomers, for example styrene, acrylonitrile, isobutylene and methyl methacrylate. In addition, certain specialty elastomers which depend upon the presence of active halogen for Vulcanizates but are not commonly regarded as sulfur vulcanizable are cross-linked by the agents of the invention, for example. chlorobutyl rubber, chlorosulfonated polyethylene and polychloropropene, commonly called neoprene. The nature of the cross-link and the mechanism by which it is formed in specialty rubber is unknown. The cross-link agents are, of course, applicable to mixtures of diene and specialty rubber.

Rubber stocks containing the cross-linking agents of this invention are suitable for bonding to natural or synthetic textile materials. The use of bonding agents commonly used for the particular filament is recommended. Generally, by using the conventional adhesive systems good adhesion is obtained with continuous or discontinuous filaments of cotton, rayon, nylon, glass, polyester or steel. The degree of adhesion obtained varies somewhat from cross-link agent to cross-link agent and sometimes mixtures of two or more cross-link agents give better adhesion.

It is particularly advantageous to use the crosslinking agents of this invention in stocks which will be in contact with polyester fiber. Certain accelerating and vulcanization systems are known to have a deleterious effect toward polyester aged stability. However, polyester fibers bonded to rubber cross-linked with the subject cross-linking agents show excellent strength retention even after aging at elevated temperature.

For the rubber stocks tested and described herein as illustrative of the invention, Mooney scorch times at 121 and 135C are determined by means of a Mooney plastometer. The time in minutes (1 required for the Mooney reading to rise five points above the minimum viscosity is recorded. Longer times on the Mooney scorch test are desirable because this indicates greater processing safety. Cure characteristics are determined at the designated temperatures by means of the Monsanto Oscillating Disk Rheometer which is described by Decker, Wise and Guerry in Rubber World, December I962, page 68. From the rheometer data, the minimum torque, R min., in rheometer units is recorded. The increase in torque is a measure of the degree of vulcanization and is proportional to the cross-link density. The time, t in minutes for a rise of two rheometer units above the minimum reading of the rubber sample and the time, required to obtain a torque of 90% of the maximum is recorded. The difference, 2 -2 is a measure of the cure rate of the sample. Vulcanizates are prepared by press curing at the selected temperature for the time indicated by the rheometer data to obtain optimum cure. The physical properties of the vulcanizates are measured by conventional methods.

PREFERRED EMBODIMENTS PREPARATION OF COMPOUNDS The compounds are prepared by reacting a polysulfenyl chloride with a thiol, a thioic acid or alkali metal salt of a thioic acid. The polysulfenyl chloride intermediate is prepared by reacting chlorine with a polythiol.

A typical procedure for preparing sulfenyl chloride intermediate is as follows: l,2-ethanedithiol (94 g., 1.0 mole) and 1000 ml. of benzene is placed in a 2 liter flask equipped with a condenser, stirrer and gas inlet tube. To the stirred solution maintained at 25C by a water bath, ther is added 1.0 mole of chlorine at the rate of about 1 gram per minute. At first a colorless solid precipitates but as the chlorine addition continues, the precipitate dissolves and a clear orange solution is obtained when all the chlorine is added. Then, ml. of benzene is removed on a rotary evaporator. The resulting benzene solution of 1,2-ethanedisulfenyl chloride is ready for use as a reactant without further purification. Other sulfenyl chloride solutions are prepared by analogous procedures. Sometimes, it is desirable to conduct the chlorine addition at lower temperatures, often C is satisfactory. Also, solvents other than benzene may be used and sometimes are preferred.

In a three liter flask equipped with stirrer, condenser and funnel is placed 80 g. (2.0 mole) of sodium hydroxide, 1040 g. of water and 360 ml. (2.0 mole) of 25% aqueous dimethylamine. The solution is cooled to C and 152 g. (2.0 mole of carbon disulfide is added to the stirred solution over a 45 minute period. When the addition is complete, the temperature bath is removed and stirring is continued for 90 minutes. The l,2-ethanedisulfenylchloride solution prepared above is added to the aqueous solution of sodium dimethyldithiocarbamate over a l-hour period while maintaining the temperature at 2040C. The mixture is stirred 1 additional hour. The precipitate which forms is collected by filtration, washed with water and dried to give 235 grams (71% yield) of 1,2- bis(dimethylthiocarbamoyldithio)ethane. The product recrystallized three times from toluene is a pale yellow solid, m.p. 141.5143C. Identification is confirmed by nuclear magnetic resonance spectral analysis. NMR: 3.55, broad singlet 12H); 3.17, singlet (4H). A Varian A-6ONMR spectrometer is used for all NMR measure ments and the absorption bands are reported using the delta scale.

The above preparation is illustrated by the following equation:

s ClSCH CH SC1 2 Nas&u(cr1 In a similar manner other dithiocarbamate-sulfenyl chloride derivatives are prepared. in case of liquid products, the solvents are removed by evaporation. The compounds and their properties are given in Table 1.

An alternative procedure comprises preparing the compounds via Bunte salt intermediates. For example, a Bunte salt is prepared by refluxing for 1 hour sodium thiosulfate pentahydrate (0.22 mole) and trans-l,4- dhchlorolZ-butene (0.1 mole) in 100 ml. of water and 70 ml. of ethanol. The ethanol is vacuum stripped and 200 ml. ofwater added. Sodium acetate trihydrate (0.3 mole) and 20 ml. of 3571 aqueous formaldehyde are added to the Bunte salt solution. To this mixture, there is added dropwise over 30 minutes with stirring, sodium hexahydro-lH-azepin1-ylthiocarbothiolate at room temperature. After stirring 1.5 hours, the oily product is extracted with chloroform, washed with water, dried with sodium sulfate and vacuum stripped. 1,4- Bis(hexahydro-lH-azepin-l-ylthiocarbony1dithio)-2- butene is recovered.

Similarly, the reaction of the Bunte salt of a,a-dichloro-p-xylene gives the following compounds: a,a-bis-N,N-dimethylthiocarbamoyldithio)-p-xylene, m.p. 155C. a,a-bis(N,N-diethylthiocarbamoyldithio)-pxylene, m.p. 1 19122C. a,a'-bis(N,N diisopropylthiocarbamoyldithio)-p-xy1ene, m.p. 158-l60C. a,a'-bis(N,N-di-n-butylthiocarbamoyldithio)-p-xy1ene, m.p. 5456C. a,a'-bis(N,N dicyclohexylthiocarbamoyldithio)-p-xy1ene, mp

-95C. a,a'-bis( pipe ridinothioca rbonyldithio )-p xylene, m.p. l25238C. a,a-bis(2,6-

(CH3) ncsscn ca ssi'zu (CH3) 2 dimethylmorpholinothiocarbonyldithio)-p-xylene, m.p.

TABLE I Melting Compound Point, C NMR l,2-bis(N,N-di-n*pr0pylthio- 87-88" 38 very broad (8H); carhamoyldithio)ethane 3.17 singlet (4H);

1.4-2.1 mu1tiplet(8H)', 0.97 triplet (12H) 1,1 '-bis(N.N-dimeth Ithio- 90.5-91.5 3.77 triplet; 3.55 carbamnyldithio )-2,. singlet; 3.05 triplet oxydiethane 1.21mihexahydro-lH-azepin- 4.1 mult. (8H); 3.16 1y1thiocarbonyldithio) sin let (4H); 1.8 ethane* mu t. (16H) I,Zbis(N-butyl-N-ethylthio- Liquid 3.8 singlet; 3.17 carhamoyldithio)ethane singlet; 2.0 mult;

1.0 mult.

1,2h1st N-cyc1ohexyl-N n Oil 3.7 mult; 3.15 propylthiocarbamoylsinglet; 2.0 mu1t.; dithiolethane 1,0 triplet 1,2-bis(N,N-diisopropylthio- 127.5- 4.8 broad; 3.1 carbamoyldithio)ethane 128.5 singlet; 1.5 doublet I.2-bislNN-dmthylthrocar- 100-102" 4.0 mull. (8H); 3 17 hamoyldlthiojethane singlet (4H); 1.3

triplet (12H) 1 1-h|stmuipholmothnrenrhunyl ()il 4 1 muIL; 31 mult, illthiolpropnnc 3 1 mult, 2.2 mull.

u.a'-b|s(morpholmothiocar- 149 7.2 singlet; 4.1 mult., honyldlthioj-p-xylene 3.75 niult.

l,2 bis( l-pyrrolidinylthio- -161" 3.8 mult.; 3.17

TAB LE 1- Continued Melting Lonipound Point. L NMR earbonyldithio)ethane singlet; 2.1 mult.

l.lblstpiperidinothio- 155-157 4.15 singlet; 3.17 carbonyldithiojethane singlet; 1.7 singlet 1.Z-bisl(2.6-dimethylmorpholino- 144-146" 5.0 mult.; 3.8 mult.; thiocarbonyldithio]ethane 3.15 singlet; 1.25

doublet a.a'-his(piperidinothiocarbonyl- 118-120 7.2 mult.; 4.1 mult.; ilithim-m-xylene 1.7 mult.

a a'-b|s( l-pyrrolidinylthio- 170 7.3 mult.; 4.1 singlet; eurbonyldithioJ-p-xylene 4.1-3.4 mult.; 2.1-

1.8 mult.

2.94111 l-pyrrolidinylthio- Glass 4.0 mult.; 3.0-1.0 earbonyldithio)-p-menthane mult.

l 2 di(N.N-dimethylthiocarbamoyl- Oil 7.33 singlet (5H); dithio l-l-phenylethane 5.2, 5.35 triplets (1H);

3.5-3.7 mult. (2H); 3.4 singlet (12H) mu bist hexahydro-lH-azepin-l- 148-150 722 single (4H); tlthloeurbamoyldithiol-p- 4.0 singlet (4H); nlcne 3.7-4.3 mult. (8H);

1.4-2.1 mult. (16H) l.I-dtthexahydro-lH-azepin-l- Oil 3.7-4.3 mult. (8H); .lthiocarbamoyldithioj-n- 2.9-3.4 mult. (3H); hexane 1.2-2.2 mult. (22H);

0.92 triplet (3H) 1.1-dlt hexahydro-lH-azepin-l- Oil 3.8-4.4 mult. (8H); ylthiocarhamoyldithio)-n- 2.9-3.5 mult. (3H); octane l. 2.2 mult. (26H);

0.88 triplet (3H) 1.1-dilhexahydro-lH-azepin-l- Oil 732 singlet (5H)); ylthiocarbamoyldithio)-l- 5.2 triplet (1H); phenylethane 3.3-4.25 mult. (H);

1.3-2.05 mult. (16H) Retry lallized from isuprnpyl alcohol "Rt-t n \tullued from heptanc/toluene "Retnstrilli/ed from heptune heniicul analysis give 43 65% (I 6.2171 H. 6 53 N and 43.8071 S compared to 43.60% C, 6.407: H

Bis-dithiocarbamates from primary amines are similarly prepared. For example, addition of 1,2- ethanedisulfenyl chloride solution to an aqueous solution of sodium benzyldithiocarbamate gives nearly a quantitative yield of 1,2-bis(N-benzylthiocarbamoyldithio)ethane, mp. lO5-l 10C, decom., NMR 7.3 singlet. 4.9 mult., 3.4 singlet and 3.15 singlet.

An alternative procedure for preparing the bis(dithiocarbamate) cross-linking agents comprising reacting carbon disulfide with a bis sulfenamide as described by Dunbar and Rogers. 1. of Org. Chem. 35, 279 (1970). who indicated that they prepared bis(morpholinothi0carbonyldithioJpentane by this reactionv For example, l.2-his(morpholinothio)ethane is prepared by adding ll-ethanedisulfenyl chloride ((1.4 mole) prepared as previously described in 275 ml. of benzene to a stirred solution of 139.2 g. of morpholine and 100 ml. of benzene at 35C over a 20 minute period. The mixture is stirred 1 hour and the precipitate collected by filtration. washed with water and dried. The l,2-bis(morpholinothio)ethane melts after recrystallization from toluene at |08.7-l09.5C. The l,2-bis(morpholinothio )cthane. 7.92 g. (0.03 mole) and 50 ml. of carbon disulfide are charged into a flask equipped with a condenser; and the mixture is heated at reflux for minutes. An additional charge of ml. of carbon disulfide is added to the reactor and the mixture is refluxed an additional 30 minutes; after which time the mixture is cooled and allowed to stand overnight. A colorless precipitate is recovered by filtration and air dried. A yield (11.2 g.) of l,2-bis(morpholinothiocarbonyldithio)ethane, mp. 169C, is recovered. NMR: 4.1-4.3 mult. (81-1); 3.7-3.9 mult. (8H); 3.18 singlet (4H).

Substituting l,6-bis(morpholinothio)hexane in the above procedure gives 1 ,6- bis(morpholinothiocarbonyldithio)-hexane, m.p. 92-93C, recrystallized from toluene-heptane. NMR:

4.1-4.3 multiplet (8H); 3.7-3.9 multiplet (8H); 2.88

triplet (4H); 1.4-1.8 multiplet (8H). Substituting 2,2- bis-(morpholinothio)oxydiethane in the above procedure gives 2,2-bis(morpholinothiocarbonyldithio)oxydiethane, an oil at room temperature. NMR: 4.1-4.3 mult. (8H); 3.6-3.9 mult. (8H); 3.08 triplet (4H).

Reaction of carbon disulfide with the di(m0rpholinothio)benzenes of Feher et a1., Z. Naturforsch 26b, 67 1971 gives the corresponding dithiocarbamate crosslinking agents with an aromatic bridging group.

Cross-linking agents with azole accelerating moieties may be prepared by condensing a polysulfenyl chloride with a 2-mercaptoazole in the presence of an acid acceptor, or with an alkali metal salt of a mercaptoazole. Alternatively, 2-azo1ylsu1feny1 chloride, for example, Z-benzothiazolylsulfenyl chloride, may be condensed with a dithiol, preferably in the presence of an acid acceptor. to give the desired bis-compounds. The following preparations illustrate suitable synthesis procedures.

lnto a 2 liter glass reactor equipped with a stirrer. condenser and funnel is charged 175 g. (1.0 mole) Z-mercaptobenzothiazole (9. 7: purity). 500 ml. of benzene and 122 g. (1.01 mole) of collidine. 1.2- Ethanedisulfenyl chloride (0.5 mole) is added slowly over 45 minutes to the stirred mixture at C. After stirring the mixture 5 hours at room temperature. the solids are slurried in 2 liters of water to remove the collidine hydrochloride, collected on a filter. washed with 500 ml. of 1% aqueous HCl. 500 ml. of water and 1000 ml. of 1% aqueous sodium hydroxide and dried. 1,2- bis(2-benzothiazolyldithio)ethane. m.p. ll9-120.5C rercrystallized from benzene. is obtained. NMR: 7.7-8.0 mult. (4H); 7.3-7.5 mult. (4H); 3.36 singlet (4H).

Substituting 2-mercaptothiazoline in the above procedure gives l.2-bis(2thiazolinyldithio)ethane. a colorless solid. m.p. l0l.5-l02C. recrystallized from heptane. NMR: 4.4 triplet; 3.4 triplet; 3.2 singlet. Substituting 2-mercaptothiazole gives l,2-bis(2-thiazolyldithio)ethane.

Using 4.5.6.7(tetrahydro)-2-mercaptobenzothiazole as the reactant gives l.2-bis[ 2(4.5,6.7- tetrahydro)benzothiazolyldithiolethane. a tan solid. m.p. 9l-93C. NMR: 3.25 singlet (4H); 2.70 mult. (8H); 1.8 mult. (8H). 2-Mercapto-4-methylthiazole gives 1.2-bis[2(4methylthiazolyl)dithiolethane. paste. brown liquid. NMR: 7.5 mult. (2H); 3.26 singlet (4H): 2.32 doublet (6H). 2-mercapto-4-methyl-5-carboethoxythiazole gives 1.2-bislanalyses 2(4-methyl-5- carboethoxythiazolyl)dithiolethane, a brown oil. NMR: 4.2 triplet (4H) J=7 cps; 3.24 singlet (4H); 3.0 triplet (4H) J=7 cps; 2.20 singlet (6H); 2.0 singlet (6H).

Reacting 2-mercaptobenzoxazole with 1.2- ethanedisulfenyl chloride in the presence of pyridine gives 1.2-bis(2'benzoxazolyldithio)ethane. a white solid. m.p. l24-125C recrystallized from petroleum ether-chloroform.NMR:7.167.6 mult. (8H); 3.43 singlet (4H SO Similarly. reacting a.a'-p-xylenedisulfenyl chloride with 2-mercaptobenzothiazole gives a.a'-bis(2- benzothiazolyldithio-p-xyleneI1.1'-bis(2- benzothiazolyldithio)-p-phenylenedimethane], m.p. l41-l42C recrystallized from dioxane. NMR: 1.7-8.0 mult. (4H); 7.3-7.5 mult. (8H); 4.12 singlet (4H). Another preparation recrystallized twice from toluene analyzes 52.86% C. 2.91% H, 5.69% N and 38.31% S compared to 52.76% C. 32271 H. 5.597? N and 38.477: S calculated for C H N s Similarly. reacting a.a-o-xylenedisulfenyl chloride with 2-mercaptobenzothiazole gives a.a'-bis(2- benzothiazolyldithio)-o-xylene. a red oil. NMR: 8.0-7.0 mult.; 4.75-4.40 mult.

Using 2-mercapto-4-methylthiazole gives, oz.oz'-bis[2- (4-methylthiazolyldithio)l-p-xylene, a tan solid. m.p. 67-69C recrystallized from ethanol. NMR: 7.1 singlet (4H); 6.7 mult. (2H); 4.0 singlet (4H); 2.3 singlet (6H).

Using a.a-m-xylenedisulfenyl chloride as the reactant gives a.a'-bis(Z-benzothiazolyldithio)-m-xylene. a tan solid. m.p. 94-96C. NMR: 8.0-7.0 mult. (12H); 4.1 singlet (4H).

l.2-Ethanedisulfenyl chloride (0.2 mole) in ml. of benzene is added over a period of one hour to a stirred mixture of 2-mercaptobenzimidazole (60 g.. 0.4 mole). pyridine (0.4 mole) and 550 ml. of benzene while the temperature is controlled between 25-30C. During the addition. a white precipitate forms. After stirring the mixture 2 additional hours at room temperature. the precipitate is recovered by filtration. A buff colored solid is obtained. m.p. 250275 C. SO which is the HCl salt of the desired product. The solid is slurried in 1 liter of water containing 100 grams of sodium bicarbonate and the mixture stirred for one hour. The precipitate is recovered by filtration and washed with water. The material is reslurried in 500 ml. of methanol and the mixture stirred 30 minutes. The product is recovered by filtration to give 67.5 grams of 1.2-bis(2-benzimidazolyldithio)ethane. m.p. -192(. NMR: 7.1-7.7 mult.: 6.5 broad: 3.42 singlet. Infrared spectral analysis shows no thiocarbonyl. a NH group 3380 cm and S-(H- groups 2780 cm l-Phenylethane-l.Z-disulfcnyl chloride (0.72 mole) in 50 ml. of benzene is slowly added over one hour to a mixture of 2-mercaptobenzothiazole (23.3 g.. 0.14 mole) and 32 m1. of pyridine in 100 ml. of benzene at 25-30C. After stirring for two hours at room temperature. the pyridine hydrochloride is separated by filtration and the mixture washed five times with 200 ml. portions of water. The benzene layer is dried over so dium sulfate and evaporated to yield an amber oil. After adding ethyl ether to the oil. 2.3 grams of 2.2-bis benzothiazolyldisulfide is recovered by filtration. The addition of petroleum ether results in an amber oil separating from the mixture. The oil is extracted three times with a mixture of 1 part ether and 2 parts petroleurn ether. After the last extraction. the residual oil is dried in vacuo to give 12.2 grams of substantially pure l.2-di(2-benzothiazolyldithio)-1-phenylethane. NMR: 7.0-7.9 mult.; 7.24 singlet; 5.14 triplet; 3.4-3.7 mult.

By a similar procedure 1.1'-bis(chlorosulfenyl)2.2'- oxydipropane (0.2 mole) prepared from 2-mercaptoisopropyl ether is reacted with 66.8 g. (0.4 mole) of 2-mercaptobenzothiazole and 33 ml. of pyridine in 500 ml. benzene to give 91 grams of 1.1 '-bis(2- benzothiazolyldithio)-2,2'-oxydipropane, an amber oil. NMR: 7.58-7.82 mult.; 7.1-7.54 mult.; 3.55-4.06 sextet; 2.98-3.23 mult.; l.17-1.5 mult.

2-Mercaptobenzothiazole (0.4 mole) is reacted with p-menthane-2.9-disulfeny1 chloride (0.2 mole) to give 2.9-di(2-benzothiazolyldithio-p-menthane. a sticky glass. NMR: 7.9-7.0 mult.; 3.5-0.8 mult.

2-Mercaptobenzothiazole 16.7 g., 0.1 mole) and triethylamine (10.1 g.. 0.1 mole) dissolved in 100 ml. of benzene is charged into a suitable reactor at room temperature and there is added dropwise while controlling the temperature between 25 and 30C 1.2-n-octanedisulfenyl chloride (0.05 mole) in 50 ml. of benzene. The reaction mixture is stirred for 1 hour and the triethylamine salt is separated by filtration. The benzene filtrate is washed three times with 200 ml. portions of water and dried over sodium sulfate. The benzene is vacuum stripped at 40C giving an oil containing a small amount of solid material. Ethyl acetate is added and 1.2 grams of 2-benzothiazole disulfide is removed by filtration. Heptane (250 ml.) is added to the filtrate and the mixture is cooled to yield 16.1 grams of 1.2- di(2-benzothiazolyldithio)-n-octane, a brown oil.

NMR: 7.15-7.95 mult. (8H); 2.9-3.5 mult. (3H); 0.86 triplet (3H); 1.0-2.0 mult. (10H).

Similarly, by reacting l,2-n-hexane disulfenyl chloride. 55 grams of an oil, identified as 1,2-di(2- benzothiazolyldithio)-n-hexane is recovered.

Chlorination of 2-ethyl bicyclo[2.2.l]heptane[5 or 6]dithiol gives the corresponding disulfenyl chloride which is reacted with two molar portions of sodium lmercaptobenzothiazole to give 2-[B-(2- benzothiazolyldithioethyl)]-5- or -6-(2- benzothiazolyldithio)bicyclo[2.2.llheptane of the formula -SS @Q/ NMR is consistent with the proposed structure.

1,2-Propane disulfenyl chloride (0.1 mole) in about 90 ml. of hexane is added to sodium Z-mercaptobenzothiazolc (38 grams) in 200 ml. of benzene at 5l0C. After warming to room temperature, byproduct is removed by filtration and the filtrate evaporated to yield a tan oil. The oil is dissolved in a mixture of toluene and heptane. White crystals slowly precipitate from the solution over a period of several days. Ten grams of 1,2- dil 2-benzothiazolyldithio)propane, m.p. 63-65C is obtained. NMR: 7.0-8.0 mult., (8H); 3.0-3.6 mult. 13H 1.5 doublet (3H).

1.3-( 2-Hydroxy)-propane disulfenyl chloride, prepared by chlorination of l,3-dimercapto-2-propanol, in about 270 ml. of dichloroethane is added to a slurry of sodium Z-mercaptobenzothiazole (38 grams) in 100 ml. of dichloroethane at C. The mixture is filtered to remove solid byproduct and the filtrate evaporated to yield an oily past. The paste is slurried in ether, filterd to remove solid byproduct, and the ether filtrate is evaporated to give 7.8 grams of a reddish, glassy product which is identified by NMR and infrared analyyses as being substantially l,3-bis(2-benzothiazolyldithio)- Z-hydroxypropane.

lb-Hexanedisulfenyl chloride (0.2 mole) in 150 ml. of carbon tetrachloride is added slowly with stirring over a period of 1 hour to a solution of 210 g. (0.4 mole) aqueous sodium 2-mercaptobenzothiazole and 250 m1. of benzene. During the addition, the temperature rises from 25 to 37C. The benzene layer is separated, dried over Na SO and filtered. The benzene is removed by evaporation to give 80.6 g. of l,6-bis(2- benzothiazolyldithio)hexane, a dark liquid. ldentification is confirmed by nuclear magnetic resonance spectral analysis NMR: 7.5 mult. (8H); 2.85 triplet 14H); 1.0-1.9 mult. (8H).

1,2-Ethanedisulfenyl chloride (0.05 mole) in 50 ml. of benzene is added at -10C to a stirred solution of the potassium salt of 2-mercapto-4-phenyl-1,3,4- thiadiazoline-S-thione (26.4 g., 0.10 mole) and 250 ml. of dimethyl formamide. The mixture is stirred for one hour and then held overnight at room temperature. Water 1500 ml.) is added to dissolve the salt. The yellow solid is collected by filtration, washed with water and dried. l,2-bis[2(4-phenyl-5-thioxo)-l,3,4- thiadiazolinyldithio]ethane (23 g), m.p. 158-l60C 34 recrystallized from dimethylsulfoxide, is obtained. NMR: 7.5 mult.; 3.1 singlet.

The following example illustrates the preparation of cross-linking agents containing a xanthogen accelerating moiety. 1,2-Ethanedisulfenyl chloride (0.1 mole) in ml. of benzene is added at room temperature to 34.8 g. (0.2 mole) of potassium isopropyl xanthate in 250 ml. of dimethylformamide. After adding one liter of water, the reaction mixture is extracted with benzene. The benzene extract is dried over Na SO and the benzene is removed by evaporation to give a yellow oil which solidifies within a few minutes. The solid is rinsed with heptane and dried to give 16 grams of 1,2- bis(isopropoxythiocarbonyldithio)ethane, a white solid, mp. 66C. NMR: 5.8 septet (2H); 3.1 singlet (4H); 1.5 doublet (12H). Chemical analysis gives 32.97% C, 5.09% H, and 52.40% S compared to 33.12% C, 5.00% H and 53.05% S calculated for C H O S 1,2-Bis[2(4,6-dimethylpyrimidinyl)dithio]ethane is prepared by adding 0.1 mole of 1,2- ethanedisulfenyl chloride in 100 ml. of benzene at room temperature to 28 grams (0.2 mole) of 2- mercapto-4,6-dimethylpyrimidine and 20 g. triethylamine in 200 ml. of benzene. The precipitate is collected by filtration, washed with water and dried. 1.2- Bisl2(4,6-dimethylpyrimidinyl)dithiolethane, m.p. -128C recrystallized from heptane is recovered. NMR: 6.65 singlet (2H); 3.2 singlet (4H); 2.2 singlet (12H).

A solution of 1,2-ethanedisulfenyl chloride (0.1 mole) in 100 ml. of benzene is added dropwise over a period of 1 hour at 25-30C to a stirred solution containing 2-mercaptopyridine (0.2 mole) and triethylamine (0.2 mole) in 100 ml. of benzene. After stirring one hour, the mixture is filtered and the filter cake washed with 300 ml. of benzene. The benzene filtrate is washed three times with 100 ml. portions of water and then dried over Na S0 The benzene is evaporated under vacuum at 40C to yield 22 grams of a red oil. The oil is precipitated twice from methylene chloride to give 16.3 grams of 1,2-bis(2-pyridinyldithio)ethane. NMR: 8.37-8.6 mult. (1H); 7.55-7.75 mult. (2H); 6.95-7.25 mult. (1H); 3.12 singlet (2H).

While controlling the temperature between 25and 30C, 2,4-dinitrobenzenesulfenyl chloride 46.9 g. (0.2 mole) is added over 42 minutes to a solution of ethanedithiol 9.4 g. (0.1 mole) and 16 ml. of pyridine and 250 ml. of benzene. The bright red slurry slowly changes to an orange color as the addition proceeds. After stirring two hours, the precipitate is recovered by filtration, washed with water and air dried. 56.3 grams of an orange solid mp. 212220C is obtained. The solid is slurried in a solution of 50 grams sodium bicarbonate and 300 ml. of H 0 and filtered to give a lighter colored solid. The solid is reslurried in 200 ml. of methanol and recovered by filtration to give 45.5 grams of 1,2-bis(2,4-dinitrophenyldithio)ethane, a yellow solid, mp. 232-235C. A number of bis(dinitrophenyldithio)alkane compounds suitable for the practice of this invention are described in J. Org. Chem., 20 50 (1955).

Similarly, 2,4-dinitrobenzenesulfenyl chloride is reacted with l-phenylethane-l ,2-dithiol to give 83% yield of 1,2-di(2,4-dinitrophenyldithio)- 1 -phenylethane, m.p. l36-l38C.

A di-Bunte salt is prepared by refluxing for 1 hour a mixture comprising sodium thiosulfate (31.6 g., 0.2 mole) in 100 ml. of water and dibromoethane (18.8 g.,

0.1 mole) in 100 ml. of ethanol. The di-Bunte salt solution while still hot is added in small portions over 10 minutes to a slurry of 2-mercapto-4.6-diallylamino-striazine (44.6 g., 0.2 mole) and 10 g. (0.25 mole) sodium hydroxide in 300 ml. of water. During the addition the temperature of the mixture rises from 25 to 40C. The mixture is stirred at 40C for 1.5 hours after which it is filtered to remove 6 grams of unreacted triazine. 120 Grams of sodium chloride is dissolved in the filtrate and the mixture allowed to stand overnight. A white solid. 24 grams, is recovered by filtration. The solid is dissolved in hot chloroform, and the solution concentrated by evaporation of the solvent. The addition of 100 ml. of methanol precipitates a crystalline white solid which is recovered. After drying, 12 grams of a white solid, m.p. 156-l57C. believed to be the monohydrate of l.2-[2(4,6-di[diallylamino])-striazinyldithiol-ethane is recovered. Chemical analysis gives 44.29% C. 5.35% H. 25.73% N. 22.96% S and 1.04% compared to 43.35% C. 5.41% H. 25.25% N. 23.10% S and 2.89% 0 calculated for C H N OS Molecular weight found 566 (554 theory).

Reacting 1.2-ethanedisulfenyl chloride in benzene with 2-mercapto-4,6-dipropylamino-s-triazine in water yields a white solid. m.p. l47-149C believed to be the monohydrate of 1.2-bis[2(4.6-di{dipropylamino])-striazinyldithio]ethane. Chemical analysis gives 42.99% C. 6.70% H. 25.33% N. 20.91% S. and 2.16% 0 compared to 42.70% C. 6.76% H. 24.94% N, 22.80% S and 2.80% 0 calculated for C- H N OS Molecular weight found 564 (562 theory).

Chlorocarbonylsulfenylchloride. CA. 65. 12112 (1966), 26.2 g. in 100 ml. of benzene is added at room temperature to 9.4 g. ethanedithiol. HCL evolves during the addition. A white precipitate forms as morpholine (35 grams) is added to the reaction mixture. The white solid is recovered by filtration. washed well with water and air dried. l.2-Bis(morpholinocarbonyldithio)ethane (Q NESSCH m.p. 178-l79C is obtained. NMR: 4.6 singlet; 3.0 singlet. The product is soluble in hot toluene, alcohol, dimethylformamide and ethyl acetate.

Chlorocarbonylsulfenylchloride (12.2 g. in 50 ml. benzene) is added to 4.3 grams of ethanol and the mixture heated at 50C for 1 hour. Ethanedithiol (4.4 g. in 50 ml. benzene) is added with evolution of HCL. The solvent is vacuum stripped to yield a tan oil identified as 1,2-bis(ethoxycarbonyldithio)-ethane.

o (c t1 oc'ssct1 NMR: 4.35 quartet; 3.1 singlet; 1.35 triplet, J=8 cps.

3,4-Toluenedisulfenylchloride is prepared by adding 4.7 grams of chlorine dissolved in 100 ml. of CCL to a solution of 3,4-toluenedithiol in 50 ml. of CCL The disulfenyl chloride is added at room temperature to l 1 grams of 2-mercaptobenzothiazolc and 6.7 grams oftriethylamine. The mixture is filtered and the benzene evaporated to give 11 grams of 3.4-tli(2- benzothiazolydithio)toluene. a red solid. m.p. 125-140C. NMR: 7.0-8.0 mult. (11H); 2.3 singlet (3H).

The tetrasulfenyl chloride of pentaerythritol tetra(3-mercaptopropionate) is prepared by reacting chlorine with 48.8 g. (0.1 mole) of the propionate in 500 ml. of benzene. One half of the sulfenyl chloride solution is added to a slurry of 2-mercaptoben2othiazole (33 g.) and triethylamine (20 g.) in 300 ml. of benzene. The temperature rises to 35C upon the addition. The amine salt is removed by filtration and the filtrate is evaporated to give a yellow glass. The solid is redissolved in 100 ml. of benzene and filtered to remove residual amine salt. The clear solution is evaporated to give a yellow glassy solid identified as substantially pure tetra( Z-benzothiazolyldithio)pentaerythritol propionate.

NMR: 7.8-7.2 mult. (4H); 4.17 singlet (2H); 3.3-2.7 quartet (4H).

A solution ml.. 0.05 mole) of 2-benzothiazolylsulfenyl chloride in 1,2-dichloroethane is added to 6.7 g. of 1,3-diphenyl 2,2-dithiolpropane, J. Am. Chem. Soc.. 81. 3148 1959). in 50 ml. of 1.2-dichloroethane. Hydrogen chloride evolves during the addition. The mixture is stirred for 3 hours and the liquid evaporated to give 2,2-bis( 2-benzothiazolyldithio 1 .3- diphenylpropane. a yellow glassy solid. NMR: 7.8-7.0 mult. (21H); 3.4 singlet (4H).

3-Chloro-l.2,4-thiadiazol-S-ylsulfenyl chloride. J. Org. Chem. 36. 14 1971 is added at 0C to ethanedithiol (9.4 g.) and triethylamine (20 g.) in 50 ml. of methylene chloride. The mixture is filtered to give a yellow solid. washed with water and air dried. 1.2- Bisl5(3-chloro-l.2,4-thiadiazolyldithio)]ethane, m.p. 156-157C is obtained. Chemical analysis gives 14.08% N and 48.17% S compared to 14.16% N and 48.65% calculated for C H CL N S A typical preparation of cross-linking agents of the formula s 5 (W0) -ss-tz-ss-i (012" 2 comprises combining polysulfenyl chloride and the amine or sodium salt of an 0,0-dialkylphosphorodithioic acid. Solid products are recovered by filtration. Liquid products are recovered by extraction and evaporation ofthe organic solvent. Compounds prepared by this procedure are shown in Table 11. They are also prepared from (RO) P(S)SH and a Bunte salt as described by Lorenz U.S. Pat. No. 3,035,082, May 15, 1962 who prepared (C H O) P(S)SSCH -SS(S)- P(OC H from sodium thiosulfate, methylene bro mide and (C H O) P(S)SH.

trithioyl )ethane sin let; 1.35 triplet; J=7 cps. 

1. THE METHOD OF CROSS-LINKING WHICH COMPRISES INCORPORATING INTO DIENE RUBBER A CROSS-LINKING AMOUNT OF
 2. radical of the formula
 2. The method of claim 1 where each Acc is different.
 2. RADICAL OF THE FORMULA
 2. radical of the formula
 3. radical of the formula
 3. The method of claim 1 where x is 1, each Acc is the same, n'''' is 1-11, m is zero and Y is selected from the group consisting of -O-S- and phenylene.
 3. radical of the formula
 3. RADICAL OF THE FORMULA
 4. radical of the formula
 4. RADICAL OF THE FORMULA
 4. The method of claim 1 where Z and Z'' are hydrogen.
 4. radical of the formula
 5. radical of the formula
 5. The method of claim 3 where Z and Z'' are hydrogen, n'''' is 1 and Y is phenylene.
 5. radical of the formula
 6. RADICAL OF THE FORMULA
 6. The method of claim 3 where Acc-S- is 2-benzothiazolylthio.
 6. radical of the formula
 6. radical of the formula
 7. radical of the formula
 7. radical of the formula
 7. The method of claim 6 where Y is p-phenylene, Z and Z'' are hydrogen and n'''' is
 1. 7. RADICAL OF THE FORMULA
 8. The method of claim 3 where the rubber composition also contains elemental sulfur.
 9. The method of claiM 1 which comprises incorporating in addition to AccS-Sx-R-Sx-SAcc a compound of the formula
 10. The method of claim 9 where X is 1, each Acc is the same, n'''' is 1-11, m is zero and Y is selected from the group consisting of -O-, -S- and phenylene.
 11. The method of claim 10 where Acc-S- is 2-benzothiazolylthio.
 12. The method of claim 11 where Y is p-phenylene, Z and Z'' are hydrogen and n'''' is
 1. 13. The method of claim 12 where R3 and R4 are lower alkyl and n'' is
 2. 14. The method of claim 13 where R3 and R4 are isopropyl.
 15. A composition comprising diene rubber and a cross-linking amount of AccS-Sx-R-Sx-SAcc where AccS is the same or different accelerating moiety, x is 1, 2, 3 or 4 and R is a divalent organic radical of 1 to 24 carbon atoms of the formula -(X)n -Y-(X)n -(Y-(X)n )m where each n'''' independently is 1 to 23, m is zero, 1 or 2, X is
 16. The composition of claim 15 which contains in addition to AccS-Sx-R-Sx-SAcc a compound of the formula 